1. Field of the Invention
The invention relates to the field of measuring devices. More specifically, the invention is concerned with determining angles on large diameter ducts or piping.
2. Description of the Prior Art
It is not uncommon in the installation of round ductwork and piping to make angled connections to other ducts or piping along the longitudinal surfaces of such ductwork and piping. To calculate the distance about the circumference that will produce the desired angle, the most commonly used method is as follows: Using a machinist""s combination square fitted with a slideable xe2x80x9cVxe2x80x9d-shaped center finding head, the apex or center point is located. Knowing the arc or angle desired and the diameter of the pipe, the length of the arc is calculated using the following formula:
Length=D/2xc3x97Axc2x0xc3x97k
In the above formula, D is the Diameter of the duct or pipe, Axc2x0 is the angle whose length from the center point is sought to be determined, and k is the constant 0.01745.
It is evident this procedure requires calculations and the use of a small tool that is not suited for use with large diameter ducts or pipes, hereinafter in the specification and claims collectively called duct(s) having a diameter of at least 12xe2x80x3. With large diameter ducts, the use of a machinist""s combination square with a center finding head can produce errors in measurement due to the small size of the tool in relation to the diameter of the duct being measured. For instance, typical of ductwork that connects to a large central duct is generally illustrated in FIG. 3.
In another aspect of determining angles for connecting ductwork, it often happens that an existing duct is mounted at ceiling height and it is necessary to create a connection at a place on its longitudinal surface to another duct located below or offset therefrom. When such large ducts are mounted in places that are relatively inaccessible, it is difficult to determine a center point for such ducts.
There are now available direct reading angle finders that, when moved or tilted, give a direct reading on a marked dial of the angle in degrees from a starting point, which is usually level or horizontal. Also, there are available from a number of suppliers direct digital readout angle finders. The angle finders most commonly are circular marked gauges mounted on a flat base that has at its bottom a magnet for holding the angle finder onto ferrous metal surfaces. These devices have been proposed for solving the problems described above, but since their dimension is only within the range of a few inches, they are not suited for use with large diameter ducts. To be useful in measuring angles on large diameter ducts, the measuring device should be capable of making these determinations on a wide variety of ducts having varying diameters. It should also contain marking means, either direct or indirect, for exactly marking a point on the ducts. Further, it should be capable of use on hard to reach ducts and be capable of projecting angles directly from one or more spaced apart ducts, including offset ducts.
The invention is directed to an angle finder for large diameter ducts and piping. It comprises a pair of legs having front and back sides, and top and bottom ends. The top ends are pivotally connected, thereby forming an inverted adjustable xe2x80x9cV.xe2x80x9d There is a moveable vertical center pointer, having a top and a bottom, mounted on the top end of the legs so as to bisect the xe2x80x9cVxe2x80x9d formed by the legs. Finally, there is present a direct reading angle finder mounted on the moveable center pointer. In a preferred embodiment, there is a laser mounted below the angle finder.
A preferred species of the angle finder has a horizontal pin attached to the top of the inverted adjustable xe2x80x9cV.xe2x80x9d The moveable center pointer comprises a bar, with its top having a longitudinal slot sized to ride in the pin. In this embodiment, there is provided a pair of arms of equal length having bottom and top ends. The bottom ends are pivotally connected to each other at a point below the longitudinal slot in the bar. Each of the top ends is pivotally connected to equidistant points near the top of the legs.
Further features include the bottom of the moveable center being pointed. The direct reading angle finder and the laser are fitted to a mounting plate having a front and a back. The mounting plate is located on the bottom of the front of the moveable center pointer and is rotatable. The back of the mounting plate has intersecting vertical and horizontal slots dimensioned to receive the bottom of the moveable center pointer. Also, there is provision for a lock for the mounting plate, which preferably is in the form of a spring-loaded pin.
The moveable center pointer desirably has a lock that preferably is the pin upon which the longitudinal slot rides. This pin is threaded and has a wing nut mounted thereon. A final preferred embodiment is that the legs contain slideable pads for protecting the surfaces upon which the angle finder of the invention is used.